1. Field
Embodiments relate to the adjustment of an information unit pacing credit to increase the rate of data transmission.
2. Background
Fibre Channel refers to an integrated set of architectural standards for data transfer developed by the American National Standards Institute. Fibre Connection (FICON) is a protocol of the Fibre Channel architecture and may also be referred to by the formal names of FC-SB-6, FC-SB-5, and other formal names used in other previously adopted FICON protocols. Further details of FC-SB-6 may be found in the publication, “Fibre Channel Single-Byte Command Code Sets Mapping Protocol-6 (FC-SB-6)”, Rev. 2.00, published by the American National Standards Institute (ANSI) on Dec. 9, 2015. Further details of FC-SB-5 may be found in the publication, “FIBRE CHANNEL Single-Byte Command Code Sets Mapping Protocol-5 (FC-SB-5)”, Rev. 2.0, published by ANSI on Mar. 26, 2013,
A channel is a direct or a switched point-to-point connection between communicating devices. In the Fibre Channel architecture, a FICON channel may perform the functions specified by FC-SB-6 or FC-SB-5 or other previously adopted FICON protocols to provide access to Input/Output (I/O) devices by means of control units or emulated control units. FICON channels may rely on packet switching for transferring data between communicating devices.
A channel command word (CCW) is a control block which includes an I/O request, and may refer to a structure of a specific system architecture which specifies a command to be executed along with parameters. A channel program is a sequence of one or more channel command words executed sequentially that controls a specific sequence of channel operations. FICON channels may transmit up to sixteen channel command words at a time along with the associated data for any write operations, where a channel command word and/or the associated data may be referred to as “information units” (IU). The channel command word may be referred to as a command IU, and the associated data may be referred to as a data IU. An IU may comprise a collection of data that is organized according to a particular structure depending on the function being performed or the data content. Information associated with the execution of an I/O operation and the operation of a device is transferred between a channel and a control unit as IUs. For example, in FC-SB-6, IUs may contain FC-SB-6 device-level commands, status, data, data descriptor or control information, or FC-SB-6 link-control information. If more than sixteen IUs are present in a channel program then the additional IUs are sent after a response received by the channel program.